1. Field of the Invention
The present invention relates generally to a Broadband Wireless Access (BWA) system, and in particular, to an apparatus and method for resource allocation for multicast data in a BWA system.
2. Description of the Related Art
Communication systems have been primarily developed for voice communication services, but they are also evolving to provide data services and various multimedia services. However, conventional communication systems, which are mainly directed to providing voice communication services, still have a narrow data transmission bandwidth and require a high subscription fee. For these reasons, they cannot satisfy diversified user demands. Furthermore, in line with rapid development in the communication industry and ever-increasing demands on Internet services, it is important to provide communication systems capable of providing Internet services efficiently. As a result of these trends, BWA systems having a bandwidth large enough to satisfy both the increasing user demands and provide efficient Internet services have been proposed.
In addition to providing voice communication services, BWA systems also aim at supporting a variety of low-speed and high-speed data services and multimedia application services (e.g., high-quality moving pictures) in combination. BWA systems are based on wireless media using a broadband of 2 GHz, 5 GHz, 26 GHz, 60 or GHz and are able to access a Public Switched Telephone Network (PSTN), Public Switched Data Network (PSDN), Internet network, International Mobile Telecommunications-2000 (IMT-2000) network, and Asynchronous Transfer Mode (ATM) network in a mobile or stationary environment. In other words, BWA systems can support a channel transmission rate of at least 2 Mbps. BWA systems may be classified into broadband wireless local loops, broadband mobile access networks, and high-speed wireless Local Area Networks (LANs) according to the terminal's mobility (stationary or mobile), communication environment (indoor or outdoor), and channel transmission rate.
The standardization of wireless access schemes of BWA systems is being conducted by the Institute of Electrical and Electronics Engineers (IEEE), which is one of the international standardization organizations, particularly by IEEE 802.16 and IEEE 802.20 standardization groups. The BWA systems use an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme for physical channels. That is, the BWA systems use an OFDM/FDMA scheme to transmit physical channel signals over subcarriers, thereby enabling high-speed data transmission.
The BWA system reports resource allocation information by transmitting information, such as the size of resource allocated to each user and an operation mode used for transmission of the corresponding resource, using broadcast channels such as a MAP channel and a shared (common) signaling channel. The resource allocation information indicates which resource is allocated to which user. The operation mode information includes a channel coding type, a coding rate, a modulation scheme, a packet length, a hybrid automatic repeat request (HARQ) type, and a multi-input multi-output (MIMO) scheme. TX data can be classified into unicast data transmitted to one user, multicast data transmitted to two or more users, and broadcast data transmitted to all users.
Schemes used for the transmission of the resource allocation information can be classified into a one-to-all resource allocation information transmission scheme and a one-to-one resource allocation information transmission scheme. The one-to-all resource allocation information transmission scheme transmits resource allocation information about all users using one encoding block to serially report the resource allocation information about all the users, which is adopted in the IEEE 802.16e standard. The size of the encoding block is transmitted over another broadcast channel. The one-to-one resource allocation information transmission scheme allocates resources using a plurality of small-sized encoding blocks. The number of the small-sized encoding block is transmitted over a separate broadcast channel.
In the one-to-all resource allocation information transmission scheme, a resource allocation message in the IEEE 802.16e system is formatted as illustrated in FIG. 1. Referring to FIG. 1, the number of terminal Connection IDs (CIDs) included in the resource allocation message is variable and the length of the resource allocation message is the sum of a fixed length of 44 bits and a variable length of 16×N_CID depending on the number of CIDs. The fixed length of 44 bits is the sum of bits of a Downlink Interval Usage Code (DIUC) (4 bits) indicating an operation mode for an allocated resource, an N_CID (8 bits) indicating the number of CIDs, an OFDMA symbol offset (8 bits) indicating the position of the allocated resource, a subchannel offset (8 bits/6 bits), a boosting (3 bits), the number of OFDMA triple symbols (5 bits/7 bits), the number of subchannels (6 bits), and a repetition coding indication (2 bits). Thus, the one-to-all resource allocation information transmission scheme is advantageous for multicast information allocation. However, because the one-to-all resource allocation information transmission scheme transmits the resource allocation information about all the users simultaneously at the start point of a frame in a time division multiplexing (TDM) scheme, power control is impossible and a TX latency such as for HARQ increases due to an increase in a scheduling period.
In order to solve the above drawbacks, the one-to-one resource allocation information transmission scheme transmits resource allocation information using an encoding block in units of the resource allocation information, which is proposed in the IEEE 802.20 draft standard. FIGS. 2A and 2B are tables showing an exemplary format of a resource allocation message in the IEEE 802.20 system.
Referring to FIGS. 2A and 2B, the one-to-one resource allocation information transmission scheme can allocate only one Media Access Control ID (MACID) (i.e., CID) to identify a terminal to one block. Thus, if resources are to be allocated to two or more users, that is, if resources are to be allocated for multicast data, resource allocation information blocks of the same type and equal in number to the number of users (i.e., MACIDs) are to be transmitted, leading to a waste of resource. For example, if Non-Sticky Forward Link Assignment Block (NS-FLAB) type information is allocated to four users, four NS-FLAB blocks with different MACIDs are to be generated and transmitted as shown in Tables 1 through 4. The NS-FLAB is a kind of IEEE 802.20 downlink resource allocation message, which is used to allocate a specific resource to a specific user only for a predetermined time. Herein, the Link Assignment Block (LAB) is the basic unit of an IEEE 802.20 resource allocation message.
TABLE 1FieldValueHeader (4 bits)0001MACID (11 bits)01101100101NodeID (6 bits)011011PF (6 bits)110110Duration (2 bits)00Extended Transmission (1 bit)0Reserved (2 bits)—CRC (16 bits)Calculated CRC
TABLE 2FieldValueHeader (4 bits)0001MACID (11 bits)010100100010NodeID (6 bits)011011PF (6 bits)110110Duration (2 bits)00Extended Transmission (1 bit)0Reserved (2 bits)—CRC (16 bits)Calculated CRC
TABLE 3FieldValueHeader (4 bits)0001MACID (11 bits)00001010001NodeID (6 bits)011011PF (6 bits)110110Duration (2 bits)00Extended Transmission (1 bit)0Reserved (2 bits)—CRC (16 bits)Calculated CRC
TABLE 4FieldValueHeader (4 bits)0001MACID (11 bits)11100110011NodeID (6 bits)011011PF (6 bits)110110Duration (2 bits)00Extended Transmission (1 bit)0Reserved (2 bits)—CRC (16 bits)Calculated CRC
As shown in Tables 1 through 4, a resource allocation information block includes a Header field that indicates the type of a resource allocation message, a MACID field that indicates an ID managed by a base station for discrimination between user terminals, a NodeID field that indicates a communication resource ID, a Packet Format (PF) field that indicates information about the combination of operation modes of data transmitted through the communication resources, a Duration field that indicates the duration of resource allocation, an Extended Transmission field that indicates the size of a resource allocation unit, a Reserved field that indicates dummy bits used to equalize the total message length in case of a component change in a resource allocation message block, and a Cyclic Redundancy Check (CRC) field that is used to check if there is a channel decoding error. In this case, even except for the bits of the CRC field and the Reserved field, 57 (=19×3) bits are wasted because information of the Header field, the NodeID field, the PF field, the Duration field, and the Extended Transmission field are transmitted four times. Moreover, if another packet is to be transmitted to the same four users, all of the four resource allocation information blocks must be transmitted again.